University of Colorado - Boulder
Wednesday, November 6, 2019
Polymer networks possessing dynamic covalent crosslinks constitute a class of materials with unique capabilities including the capacity for adapting to an externally applied stimulus. These covalent adaptable networks (CANs) represent a paradigm in polymer network fabrication aimed at the rational design of structural materials possessing dynamic characteristics for specialty applications and functions. Here, we explore several distinct approaches to CANs based on photochemically triggered responses. First, those in which the reversible bond formation, based on addition-fragmentation, occurs only during exposure to light will be discussed, enabling polymer network relaxation, photoinduced actuation and shape memory effects, and stress relaxation. Using liquid crystalline elastomer networks of this type, we will demonstrate the solution to fitting a square peg into a round hole, reversibly. Secondly, using thiol-thioester exchange chemistry, we will discuss the formation of a material that is capable of undergoing a bistable transition from a viscoelastic solid to a viscoelastic fluid, induced by light. Using this approach, we demonstrsate recyclability, healing, and enhanced toughness of materials based on these types of networks. Ultimately, the potential for CANs-based materials to impact numerous materials applications will be presented in light of their distinctive array of material properties.
Professor Christopher N. Bowman received his B.S. and Ph.D. in Chemical Engineering from Purdue University in 1988 and 1991, respectively. After receiving his Ph.D., he began his academic career at the University of Colorado in January of 1992 as an Assistant Professor. Since that time Professor Bowman has built a program focused on the fundamentals and applications of crosslinked polymers formed via photopolymerization reactions. He works in the broad areas of the fundamentals of polymerization reaction engineering, polymer chemistry, crosslinked polymers, photopolymerizations and biomaterials. Professor Bowman has remained at Colorado throughout his academic career and is currently the Patten Endowed Chair of the Department of Chemical and Biological Engineering as well as a Clinical Professor of Restorative Dentistry at the University of Colorado at Denver.